The purpose of this project is to investigate the neural controls of precocial sexual behavior in domestic chicks. Data are also being collected in order to determine how endocrine and behavioral variables influence the development and neuro-ontogenesis of sex-steroid brain systems. Studies from the project have shown that the periventricular areas of the preoptic-hypothalamic continuum contain hormone receptor neurons which are involved in the control of copulatory activity. Lesions within this network have disrupted sexual behavior, as have similarly placed chemical brain implants of progesterone. Autoradiographic data have shown that a number of neurons within the preoptic-hypothalamic continuum are sensitive to circulating radioactive testosterone. Results from all our studies suggest that the medial preoptic area is especially critical for copulatory sequence displays. We are also using the autoradiographic technique to study the concept of "neuronal plasticity," i.e., the effects that behavior has on neural development. Specifically, we are investigating the influence of precocial copulation and/or hormone priming on neuro-ontogenesis by manipulating early behavioral and hormonal experience and surveying for differential uptake of testosterone in localized neuroanatomical areas.